This disclosure generally relates to circuit breakers having a trip unit. More particularly, this disclosure relates to methods and devices for optimizing power consumption of trip units containing microprocessors.
Electronic trip units are used to actuate the separable contacts in a circuit breaker to protect electrical equipment from damage due to irregularities (e.g., excessive current flow) in the power system. The circuit breaker typically includes voltage and current sensors that provide analog signals indicative of the power system. These signals are provided to the electronic trip unit, which typically compares the signals to predetermined protection parameters. Based on the comparison, the trip unit provides instantaneous protection by means of analog circuitry and higher levels of protection by means of a microprocessor.
U.S. Pat. No. 6,167,329 to Engle et al. provides a trip unit that includes a first microprocessor and analog to digital converter for managing circuit protection, but a second microprocessor and analog to digital converter for managing voltage protection and monitoring.
Thus, prior trip units require either two microprocessors to manage both instantaneous and higher level circuit protection functions, or require a microprocessor and solid-state circuitry to manage both instantaneous and higher level circuit protection functions.
A method is provided for optimizing the power consumption of a trip unit. The method comprises sensing a first output from a power system, the first output including a first current and a current-sensing signal; supplying a power supply with only the first current, or with a second current alone or in combination with the first current; powering a microprocessor from the power supply; inputting a second output to the microprocessor indicative of whether the power supply is receiving the second current; operating the microprocessor at a first state when the second output indicates the power supply is not receiving the second current; and operating the microprocessor at a second state when the second output indicates the power supply is receiving the second current alone or in combination with the first current.
A trip unit comprising a microprocessor, an analog-to-digital converter, and a power supply is provided. The microprocessor is operable at either a first state or a second state, where the second state requires more power than the first state. The analog-to-digital converter is operatively connected to the microprocessor. The converter receives a current-sensing signal and provides this signal to the microprocessor. The power supply receives either a first current, or a second current alone or in addition to the first current. The power supply provides an output to the microprocessor indicative whether the power supply is receiving the second current. Here, the microprocessor adjusts between the first and second states depending upon the output.
A circuit breaker comprising a trip unit, and a current sensor is provided. The trip unit includes a microprocessor and a power supply. The current sensor provides a current-sensing signal to the microprocessor and a first current to the power supply. The circuit breaker further comprises an output from the power supply to the microprocessor. The output is indicative of whether the power supply is receiving the first current, or a second current from an auxiliary power source alone or in addition to the first current. The microprocessor operates at a first state when the power supply receives only the first current, but operates at a second state when the power supply receives the second current alone or in addition to the first current.
A control algorithm for a trip unit is provided. The algorithm comprises a first decision node configured to determine whether to operate a microcontroller in a first state if no auxiliary current is provided to a power supply of the trip unit and to operate the microcontroller in a second state if the auxiliary current is provided to the power supply. The first state consumes a first level of power by executing only a set of basic protection features. The second state consumes a second level of power by executing the set of basic protection features and a set of functional features.
The above-described and other embodiments, features and advantages are appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims.